1. Technical Field
The present invention relates to an electric circuit and a test apparatus. More particularly, the present invention relates to an electric circuit that outputs a recovered clock synchronized with a given periodic signal and a test apparatus that tests a device under test by means of a recovered clock obtained by regenerating an output signal output from the device under test.
2. Related Art
A test apparatus acquires an output signal output from a device under test through a timing comparator, and decides the good or bad for the acquired signal. When testing a device outputting an output signal in accordance with the application of an input signal, the test apparatus acquires the output signal at a timing at which a reference signal is delayed by the time according to a system timing. In addition, the system timing is a time interval between outputting a generation instruction for a certain test signal and really outputting this test signal from the test apparatus, and is determined by a process delay to generate the test signal by the test apparatus, a delay amount of a wire, and so on.
Moreover, when testing a device outputting a signal including therein a clock, the test apparatus acquires an output signal at a timing according to a recovered clock recovered from the output signal, as disclosed, for example, in Japanese Patent Application Publication No. 2005-285160. In this case, the test apparatus can acquire an output signal without delaying a recovered clock by the time according to a system timing.
Meanwhile, when acquiring an output signal not including therein a clock and an output signal including therein a clock output from the same device under test in a switching method, the test apparatus cannot switch the output signals with high precision because acquisition timings before and after switching may be largely off.